Albert Barnes Commentary 1 John 4:13

"hereby we know that we abide in him and he in us, because he hath given us of his Spirit." — 1 John 4:13 (ASV)

Hereby know we that we dwell in Him. Here is another, or an additional evidence of it.

Because He has given us of His Spirit. He has imparted the influences of that Spirit to our souls, producing love, joy, peace, long-suffering, gentleness, goodness, faith, etc. (Galatians 5:22–23).

It was one of the promises which the Lord Jesus made to His disciples that He would send the Holy Spirit to be with them after He should be withdrawn from them (John 14:16–17, John 14:26; John 15:26; John 16:7). One of the clearest evidences we can have that we are the children of God is derived from the influences of that Spirit on our hearts. See this sentiment illustrated .